1. Field of the Invention
The present invention relates to a method of forming a metal fastener, in particular a method for cold forging high strength fastener with austenitic 300 series material.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional method 1 of manufacturing a fastener comprises a sequence of procedures, which include a procedure of preparation 11, a procedure of head formation 12, a procedure of drill point formation 13, a procedure of threads formation 14 and a procedure of heat treatment 15; wherein, a raw shaft 21, made of the austenitic 302 or 304 stainless steel, is initially arranged in the preparation 11 and provides with a first diameter “d” for instance the specification of #12 (approximately of 5.5 mm) and a maximum shearing force approached 2630 pounds. Further, the raw shaft 21 respectively forms a head 23 and a shank 24 extended therefrom and thereafter forms a drilling portion 25 disposed reverse to the head 23 by the formation procedures 12 and 13. Still, a plurality of threads 26 are sequentially convolved on the shank 24 by a thread roller machine, thus obtaining a preliminary fastener. Ultimately, the fastener is susceptible of carburizing and quenching inside a heat furnace for altering the molecular arrangement thereof and is also coated with a carburized layer 27 thereon for increasing the hardness thereof. The above apparatuses here are omitted in Figures.
However, the conventional method may have some disadvantages:
1. Higher Manufacturing Cost and More Procedures
Although the integral fastener includes higher strength than the raw shaft through the concatenating procedures of formations, the fastener still requires the heat treating procedure to enhance its case hardness, so that the fastener can be smoothly drilled into objects. Additionally, the fastener would facilely become rusty and corrosive by the carburized layer and the additional process for corrosion resistance is necessary, whereby the conventional method results of increasing the cost and adding more excess manufacturing procedures.
2. Descending the Quality of the Fastener
The procedure of heat treatment may assist the fastener to increase its case hardness but may negatively soften its core hardness susceptible of the high temperature in carburizing and quenching, thus decreasing the elongation of the fastener to result in the broken thereof or difficultly drilling the fastener into objects. Therefore, it would affect the screwing security.